Non-constant access to image data.

Sometimes something needs to modify the data (in similar way it modifies
e.g. MeshData) and there is no reason to forbid that, as the data must
be non-const for delete[] operator anyway. There might be slight problem
with ImageWrapper, which should be able to wrap const data, but
currently nothing needs it.

src/Image.h

@@ -76,7 +76,8 @@ template<size_t imageDimensions> class Image: public AbstractImage {
         inline constexpr const Math::Vector<Dimensions, GLsizei>& dimensions() const { return _dimensions; }
 
         /** @brief Pointer to raw data */
-        inline constexpr const void* data() const { return _data; }
+        inline void* data() { return _data; }
+        inline constexpr const void* data() const { return _data; } /**< @overload */
 
         /**
          * @brief Set image data

src/ImageWrapper.h

@@ -81,7 +81,8 @@ template<size_t imageDimensions> class ImageWrapper: public AbstractImage {
         inline constexpr const Math::Vector<Dimensions, GLsizei>& dimensions() const { return _dimensions; }
 
         /** @brief Pointer to raw data */
-        inline constexpr const void* data() const { return _data; }
+        inline void* data() { return _data; }
+        inline constexpr const void* data() const { return _data; } /**< @overload */
 
         /**
          * @brief Set image data

src/Trade/ImageData.h

@@ -70,7 +70,8 @@ template<size_t imageDimensions> class ImageData: public AbstractImage {
         inline constexpr const Math::Vector<Dimensions, GLsizei>& dimensions() const { return _dimensions; }
 
         /** @brief Pointer to raw data */
-        inline constexpr const void* data() const { return _data; }
+        inline void* data() { return _data; }
+        inline constexpr const void* data() const { return _data; } /**< @overload */
 
     private:
         std::string _name;